<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        .outer {
            height: 100px;
        }

        .left {
            float: left;
            width: 100px;
            height: 100px;
            background: tomato;
        }

        .right {
            float: right;
            width: 200px;
            height: 100px;
            background: gold;
        }

        .center {
            height: 100px;
            margin-left: 100px;
            margin-right: 200px;
            background: lightgreen;
        }

    </style>
</head>
<body>
<div class="outer left"></div>
<div class=" outer right"></div>
<div class=" outer center"></div>

</body>
</html>